CODEWITHSUNDEEP
makefile
Tony Tannous
Tony Tannous

Reputation: 14876

collect all .o in subdirectories - makefile

I have the following hierarchy:

+ makefile
|
+ TT_Project1
|      obj/
|      makefile
+ TT_Project2
|      obj/
|      makefile
+ TT_Project3
|      obj/
|      makefile

The top level makefile calls recursively all makefiles below it, each compiles the .cpp to .o and places it under /obj

I would like to collect all .o in the top level to create a static library. And failing as my output library is too small...

TT := libTT.a

SUBDIRS := $(wildcard */.)
OBJECTS := $(wildcard $(addsuffix *.o,$(SUBDIRS)/obj))

all: $(TT) $(OBJECTS)

$(TT) : $(OBJECTS)
    ar rcs $(TT) $(OBJECTS)

$(SUBDIRS):
    $(MAKE) -C $@

I can clearly see that it's running the makefiles beneath it, and they are placing the *.o under their /obj as expected. But I am failing to grab all the .o I guess... any help is appreciated.

Upvotes: 0

Views: 245

Answers (1)

MadScientist
MadScientist

Reputation: 100836

First, this is wrong:

OBJECTS := $(wildcard $(addsuffix *.o,$(SUBDIRS)/obj))

Not only are you missing a / between the obj and *.o, but you need to put the /obj in the first argument to addsuffix. Suppose SUBDIRS ends up as foo/. bar/. baz/.. Then the addsuffix will expand to:

$(addsuffix *.o,foo/. bar/. baz/./obj)

which gives:

foo/.*o bar/.*.o baz/./obj*.o

which is clearly wrong. You want this:

OBJECTS := $(wildcard $(addsuffix /obj/*.o,$(SUBDIRS)))

However, that isn't what you want. It won't work because these variables are expanded when the makefile is read, before any actions have been taken. Before the makefile actually builds anything, there will be no .o files existing, which means the wildcard function will match nothing.

In your case that's a good thing, because if it did match anything you'll get errors because make doesn't know how to build those objects: they're built by the sub-makes.

But, since you have nothing that depends on the SUBDIRS target they won't get built anyway: those recipes will never run.

The easiest thing you can do is something like this:

TT := libTT.a

SUBDIRS := $(wildcard */.)

all: $(TT)

$(TT) : $(SUBDIRS)
        ar rcs $(TT) $(addsuffix /obj/*.o,$(SUBDIRS))

$(SUBDIRS):
        $(MAKE) -C $@
.PHONY: $(SUBDIRS)

The downside of this is that it will rebuild the library every time you run make even if no objects have been changed. To fix that you'll have to add some complexity.

Upvotes: 1

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